Shiitake mushrooms, Lentinus edodes (Berk.) Sing., grow naturally on the dead wood of many hardwood species. In Japan, shiitake mushrooms have been cultivated on bed logs for 300 years, and today cultivation of them is an important agricultural business. In 1997, 75,000 tons of fresh shiitake mushrooms and 6000 tons of dried shiitake mushrooms were produced. Under circumstances where approx. 60% of shiitake mushrooms have been cultivated on logs, conventionally many commercial varieties have been bred for log cultivation.
Sawdust bed cultivation of shiitake mushrooms, which was begun about twenty years ago, is characterized by rapid growth in comparison with log cultivation, and so it is a better method for commercial and mass production. On the other hand, because of limited number of varieties of shiitake suitable for sawdust bed cultivation, frequently those for log cultivation are used instead. However, when these common commercial varieties for log cultivation are cultured on sawdust beds, it takes more than four months to culture, because less than three months culture may cause that either the fruit bodies do not develop, or abnormal fruit bodies without caps appear. Furthermore, in the light of yield, less than three months culture brings a poor yield.
In 1985 the breeders of this invention developed xe2x80x98Hokken 600xe2x80x99 (registration No. 1791 based on the Japanese seed and Seedlings Law). xe2x80x98Hokken 600xe2x80x99 bears normal fruit bodies after only three months culture at 20xc2x0 C. under general commercial conditions.
Following the development of xe2x80x98Hokken 600xe2x80x99, the object of this breeding is to develop a variety of shiitake adaptable to both season-off log cultivation and sawdust bed cultivation. The breeding process is described below. This breeding project was carried out from 1993 to 1998 in Mibu-machi, Shimotsuga-gun, Tochigi-ken, Japan and Tokushima-shi, Tokushima-ken, Japan.
1. One parent is xe2x80x98Hokken 600xe2x80x99 (registration No. 1791 based on the Japanese seed and Seedlings Law) and the other is xe2x80x98Hokken 603xe2x80x99 (registration No. 4343 based on the same Law). Monokaryotic hypha were isolated from fruit bodies of each parent by monospore separation.
2. Dikaryotic hypha were produced by crossing monokaryon mycelia.
3. These dikaryotic hypha were selected first on the basis of the degree of mycelial growth on PDA-media in Tokushima-shi.
4. The selected dikaryotic hypha were cultivated on sawdust media in Tokushima-shi. Finally, this new variety of shiitake mushroom was selected by evaluating the desirable cultivation characteristics.
5. At the same time, the selected dikaryotic hypha was cultivated on logs both in Tokushima-shi and in Mibu-Machi for four years, and this shiitake mushroom was proved adaptable to log cultivation as well.
This shiitake mushroom was cultured confronting with forty-nine varieties of commercially cultivated shiitake mushrooms, including the parent varieties, on PDA-media. The results showed that this shiitake mushroom formed zone lines between all varieties (but the result of culture between xe2x80x98Hokken 603xe2x80x99 was only pseudo-positive.), and proved to have genetic sex factors different from those of all forty-nine varieties.
The clones or propagules of the claimed plant are identical to the original plant in all distinguishing characteristics.
To study the properties of this shiitake mushroom, sawdust bed cultivation was conducted under the following conditions: culture at 20xc2x0 C., for 100 days; and development at 13xc2x0 to 18xc2x0 C. (a cycle of 12 hours) in 70 to 90% humidity for 80 days. Bag cutting was used for the first flush or break treatment, and soaking for the second, third and fourth treatments.
Changes in yield of the present shiitake mushroom developed by the first, second, third and fourth treatments is shown in FIG. 4 comparing with xe2x80x98Hokken 600xe2x80x99 and xe2x80x98Hokken 603xe2x80x99 as control varieties, which are for sawdust bed cultivation.
This shiitake mushroom yielded 416.3 grams of fruit bodies per bag of 1.2 kg sawdust bed and was confirmed to be suitable for sawdust bed cultivation. The number of days required between the beginning of development and the stage of peak development of this shiitake mushroom was eight days, which shows the same level as xe2x80x98Hokken 600xe2x80x99 and xe2x80x98Hokken 603xe2x80x99.
This shiitake mushroom can be asexually reproduced by subculture for a given period of time. The subculture is a common method for maintaining a mushroom strain on suitable media. Media such as PDA (potato dextrose agar) and MEA (malt extract agar) can be used as shiitake culture media, and shiitake strain can be subcultured every one to six months. To produce a spawn, fragments of the dikaryonicic mycelia grown on PDA or MEA are inoculated in sawdust or wood media, and are cultured at about 20 for one to three months. Sawdust spawn is used on sawdust beds, and sawdust or wood chip spawn is used for logs in commercial cultivation.
The outstanding characteristics of this shiitake mushroom in its cultivation on sawdust beds are: that the culture period and the number of days required until the peak development stage are equivalent to those of the standard varieties; that its yield per bag of sawdust bed is increased; and that the quality of the fruit bodies is very good.